This application proposes to study the role of the cell surface in differentiation by examining two genetic systems in the mouse--the Tla-H(Tla) system and the W system. Two approaches will be used. The first will be to examine the known cell surface antigens specified by the Tla-H(Tla) loci to determine how these antigens are recognized by the immune system and whether they have any functional significance. The second approach will be to examine the effect of the W locus, which interferes with normal differentiation on the components of the cell surface. These two approaches involve genetic linkage and allelism studies; transplantation and immunization with mouse tissues including skin, hematopoietic cells and tumor cells; passive transfers of immunity; and serological definition of cell surface antigens by cytotoxicity testing, hemagglutination and immunofluorescence techniques.